Photosensitive Ionic Nematic Liquid Crystalline Complexes Based on Dendrimers and Hyperbranched Polymers and a Cyanoazobenzene Carboxylic Acid

The synthesis and characterization of ionic liquid crystal dendrimers and hyperbranched polymers based on the ammonium salts of commercially available dendrimers poly(propylene imine) [PPI-(NH 2 ) n ] (with n = 16), and poly(amidoamine) [PAMAM-(NH 2 ) n ] (with n = 16), and random hyperbranched poly(ethyleneimine) (PEI) and the prepared fully methylated PEI (namely PEIMe) with 5-(4-cyanophenylazophenyloxy)pentanoic acid (CAzPA) are reported. The occurrence of proton transfer from the carboxylic acid to the amine groups was confirmed by IR and NMR measurements. 5-(4-Cyanophenylazophenyloxy)pentanoic acid does not show mesogenic properties. However, all synthesized ionic complexes displayed a nematic mesophase. The liquid crystalline behavior was investigated by means of differential scanning calorimetry, polarizing light optical microscopy, and X-ray diffractometry. Themogravimetry analysis was carried out in order to determine the stability of the complexes, all of which have their mesophase−isotropic liquid transition under the temperature of 5% weight loss. Birefringence has been induced using 488 nm linearly polarized light in thin films of the ionic dendritic polymers containing azobenzene moieties. High and stable values of the in-plane order parameter up to 0.67 have been reached.